The present invention relates to a multicylindrical rotary compressor constituted to be usable by switching a first operation mode in which first and second rotary compression elements perform compression works, and a second operation mode in which substantially the only first rotary compression element performs the compression work, a compression system provided with the multicylindrical rotary compressor, and a freezing device using the system.
Heretofore, this type of compression system is constituted of a multicylindrical rotary compressor, a control unit which controls an operation of the multicylindrical rotary compressor and the like. This multicylindrical rotary compressor, for example, a two-cylinder rotary compressor provided with first and second rotary compression elements is constituted by storing a driving element and the first and second rotary compression elements driven by a rotation shaft of the driving element in a sealed container. The first and second rotary compression elements include first and second cylinders, first and second rollers engaged with eccentric portions formed on the rotation shaft to rotate eccentrically in the respective cylinders, respectively, and first and second vanes which abut on the first and second rollers to divide each cylinder into low and high pressure chamber sides. The first and second vanes are constantly urged with respect to the first and second rollers by spring members.
Moreover, when the driving element is driven by the control unit, a low-pressure refrigerant gas is sucked from a suction passage into the low-pressure chamber side of the cylinder of each of the first and second rotary compression elements, and compressed by the operations of each roller and each vane to constitute the refrigerant gas at high temperature and pressure. After the gas is discharged from the high-pressure chamber side of each cylinder into a discharge sound muffling chamber via a discharge port, the gas is discharged into the sealed container, and discharged to the outside (see, e.g., Japanese Patent Application Laid-Open No. 5-99172).
In the compression system provided with such multicylindrical rotary compressor, in a case where compression operations are performed in both of the first and second cylinders in a small capability region at the time of a light load or low-speed rotation, the refrigerant gas has to be sucked as much as exhaust capacities of both of the cylinders, and compressed. Therefore, a rotation number of the driving element is lowered as much by the control unit to operate the system. However, a problem has occurred that when the rotation number excessively lowers, an operation efficiency of the driving element drops, a leakage loss increases, and a compression efficiency also drops.
Therefore, in view of such problem, a compression system is developed in which a one-cylinder operation and a two-cylinder operation are switchable depending on capability. That is, one of the spring members which urge the first and second vanes of the multicylindrical rotary compressor with respect to the first and second rollers, for example, the spring member which urges the second vane with respect to the second roller is removed, and a refrigerant pressure on a discharge side of each of the rotary compression elements is applied as a back pressure of the second vane by the control unit at the time of the two-cylinder operation. Accordingly, the second vane is urged on the side of the second roller, and the compression work is performed.
On the other hand, in the small capability region, the control unit applies the refrigerant pressure on a suction side of each of the rotary compression elements as the back pressure of the second vane. Since this suction pressure is a low pressure, the second vane cannot be urged on the second roller side. Therefore, the compression work is not substantially performed in the second rotary compression element, and the compression work of the refrigerant is performed by the only first rotary compression element.
As described above, when the one-cylinder operation is performed in the small capability region, an amount of the refrigerant gas to be compressed can be reduced, and the rotation number can be raised as much. Consequently, the operation efficiency of the driving element can be improved, and the leakage loss can be reduced.
However, in such constitution, when the two-cylinder operation is switched to the one-cylinder operation, the refrigerant pressure (high pressure) on the discharge side of each of the rotary compression elements, which has been applied as the back pressure of the second vane at the time of the two-cylinder operation, remains in a back-pressure chamber of the second vane. Much time is required until the inside of the back-pressure chamber of the second vane is switched to a low pressure. Therefore, the second vane does not easily retreat from the second cylinder, and this causes a disadvantage that the second vane collides with the second roller to generate a collision noise.
Moreover, the second rotary compression element which is not provided with the spring member has a problem that the refrigerant gas leaks from the second cylinder via a gap in the second vane during the two-cylinder operation. Especially at the time of low-speed rotation, a leak amount increases, and a remarkable drop of the compression efficiency is incurred.